1. Field of the Invention
The present invention relates to a manufacturing method of a disk substrate having a pit and a groove with different depth formed separately in the inner and outer circumference of the disk substrate, and relates to a disk substrate manufactured by the manufacturing method and a disk manufactured by the disk substrate.
2. Description of the Related Art
There existed various types of optical disks such as a read only type, a recordable type and a rewritable type. An optical disk, which is provided with a read only area and a recordable area enabling to be recorded by a user in one substrate, has been proposed and practiced. In an optical disk having a pit area to be a read only area and a groove area to be a recordable area, generally, a pit depth is set to xcex/4n, which is the maximum amplitude of a sum signal of a reproduced signal, wherein xe2x80x9cxcexxe2x80x9d is a wavelength of a laser beam for recording and reproducing and xe2x80x9cnxe2x80x9d is a refractive index of a substrate of the optical disk. On the other hand, a groove depth is set to xcex/8n, which is the maximum amplitude of a differential signal of a tracking signal. In order to obtain such an optical disk substrate as being formed in one surface with a deep pit and a shallow groove, which are different in depth from each other, it is necessary for a pit and a groove to be varied in depth while forming a photoresist pattern as one process of manufacturing an optical disk master, which is a foundation of manufacturing the optical disk substrate.
Generally, in a process of forming such a photoresist pattern, there existed the method of changing each depth of pit and groove in one substrate such that using a laser beam in stronger intensity forms a pit and using a laser beam in weak intensity forms a groove. A depth of pit is determined by a film thickness of photoresist coated on a surface of substrate. However, a depth of groove depends on an intensity of laser beam and is apt to vary by a change of laser beam intensity or focus signal. A width of groove also depends on laser beam intensity, so that it is extremely hard to obtain an arbitrary width of groove. Further, a shape of groove obtained becomes approximately a V shaped one, so that a stable tracking signal can hardly be obtained. Furthermore, a recording power for recording a signal in a groove is necessary to be more powerful than that for recording in a conventional groove having a rectangular bottom, so that such a V shaped groove is a shape of unsuitable for recording in higher liner velocity.
In order to solve the problem mentioned above, there provided the prior arts such as a method of obtaining a pit and groove having a different depth from each other as mentioned above by using a photoresist pattern having a variety of depths as mentioned above and further by using the plasma etching and ashing processes.
Accordingly, in consideration of the above-mentioned problems of the related art, an object of the present invention is to provide a method for manufacturing a disk substrate for mass production of a phase change optical disk, wherein the disk substrate is provided with a pit having a first depth and a groove having a second depth allocated in an outer circumference area of the pit, the method including the steps of coating photoresist on a surface of a glass substrate (1) so as to form a resist layer (2) on the glass substrate (1), etching the surface of the resist layer (2) in atmosphere mixed with Argon and Oxygen in ratio of 10 to 90% under gas pressure of 0.1 to 1.5 Pa, wherein a pit (p1) having a first depth and a groove (g1) having a second depth are formed on the surface of the resist layer (2), forming a depression having a first and a second depth by cutting laser to be exposed on the surface of the resist layer (2), etching the depression having the first depth and the second depth from the surface of the resist layer of the disk substrate (1) in atmosphere mixed with Argon and Oxygen in voluminal ratio of 10 to 90% under gas pressure of 0.1 to 1.5 Pa, wherein the first and the second depth of the depression become predetermined value respectively, and ashing the resist layer (2) from the glass substrate (1).
Other object and further features of the present invention will be apparent from the following detailed description when lead-in conjunction with the accompanying drawings.